This invention relates to a spotlight with an adjustable angle of radiation, or reflection, having a light source, a reflector associated with the light source, a first focusing lens (collector or converging lens) placed in a direction of beam (along a beam path) of the light source-reflector combination, and a second focusing lens placed in the beam path between the light source and the first focusing lens, whereby the reflector, the light source, and the second focusing lens are mounted as an optical unit that is movable relative to the first focusing lens along an optical axis of the spotlight, and a distance between the light source and the second focusing lens is adjustable inside the optical unit.
Spotlights with adjustable angles of radiation have been known in the prior art for a long time. These spotlights can be divided into two basic classes, namely Fresnel (stepped) lens spotlights and spotlights having very deep reflectors.
Conventional Fresnel lens spotlights each have a single echelon lens (Fresnel lens). Incandescent bulbs, halogen bulbs, or discharge lamps are used as light sources in these echelon spotlights. In such a spotlight, the light source and a reflector are mounted on a slide at a fixed distance from each other. The slide can be moved relative to the Fresnel lens. Focusing is achieved by moving the slide. However, in Fresnel lens spotlights of this type, a significant effective loss of light occurs at focus settings with small angles of reflection. Since there is no second lens to concentrate the light toward the Fresnel lens, a large portion of the light emitted by the light source is simply absorbed by an inner wall of a housing at such focus settings, which results in loss of light and unneeded heating of the housing.
In general, a spotlight with a very deep reflector is constructed so that a lamp and a reflector can be displaced relative to each other, but in these spotlights the lamp remains inside the reflector, along its optical axis, at all times. By changing a position of the lamp within the reflector, the angle of radiation of these spotlights is modified. However, a focusing path that can be achieved in this way is minimal, so that an angle of radiation can be varied only within relatively narrow limits. Spotlights of this type do provide a high degree of light efficiency, but they exhibit unfavorable light distribution in nearly all lamp positions. A reason for this generally poor light distribution is that a reflector shape provided respectively for each of these spotlights, in terms of the resulting light distribution, can be optimally designed for only a single lamp position. Uneven light distribution occurs when the lamp or the reflector are moved for focusing purposes. Therefore, to improve light distribution, replaceable front lenses are often used in spotlights of this type. These lenses may have frosted properties, a honeycomb structure, or other special design features that serve to provide additional focusing or dispersion of the light. With these spotlights, therefore, variously modified front lenses must be used for various focus settings. For many such spotlights with a very deep reflector, in fact, both the lamp and the reflector are mounted in a fixed position in a housing, i.e. the angle of radiation is modified in such cases exclusively by changing front lenses that differ in design. This entails a relatively significant amount of labor and time spent in changing the front lenses, if a spotlight of this type is used in a situation in which the focus setting must be changed often.
A spotlight with an adjustable angle of radiation that already exhibits a significant improvement over the spotlights described above is disclosed by U.S. Pat. No. 4,823,243. This spotlight has a light source, a reflector associated with the light source, a first focusing lens placed in a beam path in a direction of beam of the light source-reflector combination, and a second focusing lens located between the light source and the first focusing lens. The reflector, the light source, and the second focusing lens are mounted as an optical unit that is movable relative to the first focusing lens along the optical axis of the spotlight. Inside the optical unit, a distance between the light source and the second focusing lens is adjustable. The spotlight disclosed in U.S. Pat. No. 4,823,243 provides a large focus area (see FIG. 4 herein), and achieves a high degree of light efficiency in terms of energy required to operate the spotlight. In addition, the spotlight disclosed in U.S. Pat. No. 4,823,243 provides light distribution that is so even that a traditional concept of "bean and spread" or "conical and diffused light" can no longer be applied. As shown in FIG. 4, a characteristic illuminance (illumination intensity) curve of a lighted field does exhibit a slight shoulder, but light intensity across an entire lighted area is largely constant.
It is an object of this invention to provide a spotlight with an adjustable angle of radiation that allows even greater variability in an angle of radiation and in illuminance than do known spotlights with adjustable angles of radiation.